Report

GRINDING BASICS Presented by Dale Savington For: Bosch Rexroth – Rineer Hydraulics • Cylindrical Grinding Processes • Machine Requirements (Utilizing CBN) • Abrasives • Properties of Abrasives • Superabrasives • Bonds • Mechanics of Grinding • Coolant • Truing & Dressing CYLINDRICAL PROCESSES (GRINDING BETWEEN CENTERS) Conventional Plunge / Face Grinding • Down-Feed (face bump grind) • Q’ (Prime) 2.14 (0.2) + • Wheel Velocity • S.F.P.M. 8,500 + • m/sec. 43 + • High volume of coolant to get into grinding zone Conventional Traverse Grinding • Cross –Feed (Traverse) only • Stock Removal (in-feed depth) • 0.0” to 0.0178 mm (0.0007”) • ≥ 10% of abrasive Ø / pass • Traverse rate •10 – 25% of wheel width per rotation of part • Wheel Velocity • S.F.P.M. 8,500 + • m/sec. 43 + • Finish Grinding Peel (“Quick Point”) Grinding • Multiple grinding functions Wheel face configuration • Wheel Velocity • S.F.P.M. 17,000 + • m/sec. 86 + • Easier coolant delivery into grinding zone (narrow contact area) Cylindrical Grinding Plunge Q Prime (Q’) = work piece diameter x 3.14 (π) x in-feed rate Example: Work piece diameter = 25.4mm (1”) In-feed rate = 4.039mm/min. (0.159”/minute) Q’ then equals: (25.4 x 3.14 x 4.039)/60 = 5.37 mm3/mm· sec. 1 x 3.14 x 0.159 = 0.5 in3/in· min. Therefore: (5.37/(3.14 x 25.4)) x 60 = 4.039mm/min. 0.5/(3.14 x 1”)= 0.159”/min. infeed rate Note: (mm3/mm· sec.) to (in3/in· min.) conversion of 10.75 Surface Grinding CONVENTIONAL GRINDING Wheel Speed = S l o w Stock Removal = Light Fast CREEP FEED Wheel Speed = S l o w Stock Removal = Heavy Slow HEDG (HIGH EFFICIENT DEEP GRINDING) Wheel Speed = Fast Stock Removal = Heavy Fast Surface Grinding Q Prime (Q’) =In-feed rate/pass x Traverse rate/min. Example: In-Feed per pass= 0.0508mm (0.002”) Traverse rate per min.= 3,810mm (3.81m)/min. (150” (12.5’)/minute) Q’ then equals: (0.0508 x 3,810)/60 = 3.225 mm3/mm· sec. 0.002 x 150 = 0.3 in3/in· min. Therefore: (3.225/(0.0508) x 60 = 3,810mm/min. traverse rate 0.3/(0.002”)= 150”/min. traverse rate Note: (mm3/mm· sec.) to (in3/in· min.) conversion of 10.75 MACHINE REQUIREMENTS MACHINE RIGIDITY Spindle’s Slides Centers Head Stock Tail Stock Base Parts will Mirror Machines Rigidity Wheel Spindle POWER! Kilowatts! Wheel spindle power per 25.4mm (1”) of wheel to work contact Conventional Abrasives = 3.75 Kw (5 H.P.) CBN Abrasives = 7.5 Kw (10 H.P.) (HEDG) = 18.75 Kw (25 H.P.) Peel – depends on contact area, material and stock removal SPINDLE INTEGRITY Run-Out Out of Balance Static Balance Dynamic Balance – real time WHEEL BALANCE (DYNAMIC VS STATIC) Portable Dynamic Balance Static Balance allows balance in stationary position off the spindle. Dynamic Balance is continuous balance on the spindle at working rotating speeds. WHEEL BALANCE (DYNAMIC VS STATIC) Dressing: Sound of dresser touching wheel through coolant. Complete contact = dressed wheel Other uses: Picture of grinding process Crash prevention ACOUSTIC SENSORS MACHINE REQUIREMENTS (MAXIMIZING GRINDING PROCESS) Rigidity Coolant Flow Spindle power Smooth Transitional Plumbing Wheel Velocity Coolant Tank Capacity Rotary Dresser Coolant with lubricity Acoustic Sensors Dynamic Balancing ABRASIVES WHAT AFFECTS ABRASIVE DECISION? Ferrous Materials Non-Ferrous Materials Fatigue Concerns (Potential thermal damage) Production Numbers Dimensional Tolerances Process Controls TYPES OF ABRASIVES Aluminum Oxide Silicon Carbide Cubic Boron Nitride (CBN) Diamond ABRASIVE SELECTION Ferrous Materials Non-Ferrous Materials Cubic Boron Nitride (CBN) Diamond Aluminum Oxide Silicon Carbide PROPERTIES OF ABRASIVES ALUMINUM OXIDE (AL2O3) For Grinding Ferrous Materials Thermal Conductivity O (W/m K) = 29 Hardness on Knoop Scale (kg/mm2) = 1400 - 2100 SILICON CARBIDE (SI,C) For Grinding Non-Ferrous Materials Hardness on Knoop Scale (kg/mm2) = 2700 Thermal Conductivity O (W/m K) = 400 CUBIC BORON NITRIDE (CBN) (B,N) For Grinding Ferrous Materials Hardness on Knoop Scale (kg/mm2) = 4500 Thermal Conductivity O (W/m K) = 1300 DIAMOND (C) For Grinding Non-Ferrous Materials Hardness on Knoop Scale (kg/mm2) = 8000 Thermal Conductivity O (W/m K) = 2000 REVIEW Knoop Hardness Aluminum Oxide Silicon Carbide Thermal Conductivity 1400-2100 29 2700 400 Cubic Boron Nitride (CBN) 4500 1300 Diamond 2000 8000 THE PUZZLE WHY NOT DIAMOND? Diamond + Ferrous Material + Heat = Note: Silicon Carbide has similar reaction SUPERABRASIVES WHAT ARE SUPERABRASIVES? Diamond Cubic Boron Nitride (CBN) Borazon WHAT MAKES SUPERABRASIVES SUPER? Hardness - (Resistance to wear) Thermal Conductivity- (The ability to absorb heat) Flexibility- (one wheel for many applications) Wheel Life- (100 + times Conventional Abrasives) SOME ADVANTAGES (FOR SUPERABRASIVES) Decreased Cycle Time Reduced Dressing Reduced Gaging More Consistent Parts (Less Scrap) Reduced Time for Wheel Changes Reduced Coolant Changes Reduced Filter Changes Reduced Coolant Disposal Costs Less Swarf Contamination CONVENTIONAL ABRASIVES CONSTRUCTION Conventional Layer = full area of wheel Wheel Vitrified Bond Resin Bond Rubber Bond Shellac Bond SUPERABRASIVE CONSTRUCTION Superabrasive Layer = 3mm (1/8”) to 12.7mm (1/2”) Wheel Core Resin Bond Metal Bond Vitrified Bond BONDS GRINDING MATRIX VITRIFIED WHEEL Grain Pore Bond Chip GRINDING WHEEL BOND SYSTEMS Resin , Metal & Bonds Abrasive + Bond = Wheel GRINDING WHEEL BOND SYSTEMS Open Structure (Low fired) Vitrified Bonds Abrasive + Bond + Pores = Wheel GRINDING WHEEL BOND SYSTEMS Plated Wheels (Single Layer) Wheel body Cathode (-) Abrasive Anode (+) Electrolyte (Nickle Solution) Plated Wheel Cut-A-Way Mechanics of Grinding ABRASIVE WEAR Bond Abrasive Fracture wear Chip Cut a way of wheel Conventional Abrasive (one grain) Attritious wear (Rubbing) ABRASIVE WEAR Work Piece Conventional Abrasive (one grain) Fracture wear Work Piece ABRASIVE WEAR Conventional Abrasive (one grain) Fracture wear Work Piece ABRASIVE WEAR CBN Abrasive (one grain) Attritious wear Work Piece ABRASIVE WEAR STANDARD MARKINGS CONVENTIONAL ABRASIVES Abrasive Type Abrasive Size A C SG30 60 120 80 A 24 Abrasive (combination) 1 2 Hardness (Grade) Structure (Pore) Bond J K L 6 12 10 V V V R B STANDARD MARKINGS SUPERABRASIVES Abrasive Type Abrasive Size Hardness (Grade) Concentration Bond BN D BN 140 240 120 J k L 100 75 150 B M V Superabrasives are always combinations 120/140, 80/100 etc. Calculating concentration take number and divide by 4 Example 100 ÷ 4 = 25% by volume of abrasive in wheel COOLANT Type, Flow, Pressure & Nozzle Design COOLANT TYPES Water, Water Soluble Oils, Straight Oils Specific Gravity of each & traits for grinding: Water = 1 SG (Issue – lack of Lubricity) Water Soluble Oil = 1 SG (Issues – Foaming & bacteria) Straight & Synthetic Oils = 0.87-0.95 SG (Issues – Heat & Disposal) ( Specific Gravity (SG not a factor in calculations) ) COOLANT CONDITION Tank Size & Coolant Temp. Filtration & Particle Distribution Chemistry (Lubricity) COOLANT PRESSURE Equal Wheel Velocity Bernoulli’s Equation for Pressure ΔP (Bar) = SG x Vj2 / 200 Where:Vj2 = (M/s)2 Example: Wheel velocity – 43.3M/s (8,500 S.F.P.M.) Then: 1 x (43.3)2 / 200 = 9.4 Bar Bar conversion Bar x 14.508 = 136 psi Bernoulli’s Equations Bernoulli's Equation: P = SG x Vj2 / 535824 Where: P = psi Vj = (S.F.P.M.)2 SG = Specific Gravity of coolant 135 psi Metric Pressure (Bar) Bernoulli's Equation: ΔP = SG x Vj2 / 200 Where: ΔP = Bar 9.4 bar Vj2 = (M/s)2 SG = Specific Gravity of coolant Inch Velocity - (S.F.P.M.) Bernoulli's Equation: Vj = (19.25 x Q) / Aj Where: Vj = Velocity (S.F.P.M.) 8,075 S.F.P.M. Q = Flow rate (G.P.M.) Aj = Area of nozzle exit (in2) Metric Velocity - (M/s) Bernoulli's Equation: Vj = (103 / 60) x (Q/Aj) Where: Vj = Velocity (M/s) Q = Flow rate (Liters/min.) Aj = Exit area of nozzle exit (mm2) Inch aperture size - (In2) Bernoulli's Equation: A j= (19.25 x Q) / (CD x Vj) Where: Aj = aperture (in2) Q = GPM CD = 0.95 Vj = Velocity (S.F.P.M.) Metric aperture size - (mm 2) Bernoulli's Equation: Aj = (10^3 x Q) / (Vj x 60) Where: Aj = aperture (mm2) Q = LPM CD =0.95 Vj = Velocity (M/s) 41 M/s 2 0.03142 in 19.4 mm2 Coherent-Jet Nozzle Calculator (Dr. John Webster) Inch Metric INPUT Coolant Jet Specific Speed Gravity Required SG SFPM 1 8,500 OUTPUT Nozzle Exit Diameter inch 0.2 psi GPM pounds Coolant Specific Gravity SG 135 13 8 1 Pressure Flowrate at Nozzle Calculated GPM per H.P. Used / area Spindle H.P. (Max) 25 Conv. wheels Spindle H.P. no load Spindle H.P. full load 4 10 Some specific gravities (SG) Type of Coolant SG at 20°C Mineral oil Synth oil Water 0.87 0.95 1 Area for Rectangular Nozzle Length Height Area Metric Conversion of above #'s INPUT CBN wheels Reaction Force GPM 12 43 Spindle Kw no load Spindle Kw full load GPM 12 27 48 75 109 193 inch 0.622 0.824 1.049 1.380 1.610 2.067 5.10 Pressure Flowrate at Nozzle Pipesize schedule 40 inch 1/2 3/4 1 1-1/4 1-1/2 2 3 7.3 Some specific gravities (SG) Type of Coolant SG at 20°C Mineral oil Synth oil Water 0.87 0.95 1 LPM Newton 9.4 50.4 36.4 Round Length LPM 43.0 CBN wheels 34.4 Flowrate ID of Pipe Pipesize schedule 40 L/min 50 100 180 300 400 750 mm 16 21 27 35 41 53 inch 1/2 3/4 1 1-1/4 1-1/2 2 Calculated Area of nozzle exit in2 mm 2 0.03142 20.428 0.200 Reaction Force bar Calculated LPM per Kw Used / area Spindle Kw (Max) 18.4 Conv. wheels 9 Max. ID of Pipe Flowrate OUTPUT Jet Nozzle Speed Exit Required Diameter M/s mm 5.1 Note: The above results are for a given area. If you have multiple nozzles then if all have the same dimension the GPM or LPM must be multiplied by the number of nozzles to obtain correct needed flow rate. Copyright © 2013 [Dale Savington]. All Rights Reserved Coolant Flow Calculations Coolant Type mm or Inch Water Soluble drop down box mm drop down box Average if Multiple Nozzles of Height of Nozzle Openings Average if Multiple Nozzles Contact of wheel to Part length (Nozzle Length) Average Nozzle Diameters # of Round Nozzles Height Length 5.100 3 # of Rectangular Nozzles Diameter # of round nozzles # rectangular nozzles Grinding Wheel Rotation 1,600 Grinding Wheel Diameter 508.000 Wheel rpm Wheel Diameter Velocity % Coolant (Faster Than Wheel Velocity) Calculated Coolant Flow rate Needed Calculated Coolant Pressure Needed 41 131 Actual Measured Coolant Pressure 131 Pressure (P.S.I.) 9.0 Bar Actual Measured Coolant Flow rate Gallons Per Minute % of needed GPM 155 LPM Measured Coolant Flow Percent Compared to Calculated Velocity Needed (GPM) 41 99% Measured Coolant Pressure Compared to Calculated Pressure Needed (psi) 100% % of needed P.S.I. 43 Gallons Per Minute Pressure (P.S.I.) Calculated M/s- Velocity IMPORTANT: The calculated data is for optimum flow and pressure based on the nozzle geometry and numbers you have entered. However, you will need to be sure that the actual measured pressure and flow rate are reflective of the calculated numbers. Mechanical realities such as head loss, pump type, flow of coolant from pump etc will influence actual measurements. Optimal measurements would be Pressure Gage and Flow Meter located at Manifold 156 LPM 9.0 Bar Copyright © 2013 [Dale Savington]. All Rights Reserved Conversion Table Input Conversions mm: Inch Bar: PSI Meters per Second (M/Sec.): Liters per Minute (LPM): Pounds per Square Inch (PSI): Head loss per foot (0.3048 meters): Meters: Wheel SFPM (Note: 164 minimum needed to register): Power (Kw): Gallons Per Minute (GPM) Formulation Pressure Per Square inch (P.S.I.) Formulation Note: S.F.P.M. GPM Feed of Head Nozzle PSI Loss Feet Nozzle PSI needed H.P. Nozzle Height x Wheel S.F.P.M. x 12 (231 ÷ Wheel "P" Line) (Surface Feet Per Second (S.F.P.S.) of Wheel ÷ 12.2) 2 231 = in3/gal of H2O at Sea level (Standard Factor) For PSI a factor of 0.87 is multiplied for Oil "P" line of wheel equals the linear width of wheel COOLANT FLOW Rim Section Grinding Wheel Grinding Wheel Grinding Wheel “P” Line Work Piece Work Piece (Part) “P” Line Work Piece “P” LINE /RIM SECTION TRUING & DRESSING THE DIFFERENCE BETWEEN TRUING & DRESSING TRUING RESIN & METAL BONDS DRESSING RESIN & METAL BONDS TRUING & DRESSING PLATED WHEELS TRUING & DRESSING VITRIFIED BONDED (CBN WHEELS) EXAMPLES OF ROTARY DRESSERS Direction for Dressing with rotary Dressers Preferred (opens wheel) Closes Wheel Conventional Abrasives – Aluminum Oxide Ceramic Abrasives – Seeded Gel (SG) ≤ 0.0178mm (0.0007”) per pass ≤ 0.005mm (0.0002”) per pass CBN Abrasives ≤ 0.0025mm (0.0001”) per pass TRUING & DRESSING (DEPTH OR IN-FEED) TRUING & DRESSING (TRAVERSE RATE) Starting Parameters 0.1mm (0.004”) per revolution of wheel Assuming 0.5mm (0.020”) radius dresser Faster traverse rate creates rougher finish Slower traverse rate creates finer finish Conventional CBN Grinding Surface Finish = Grit Size Grinding: Surface Finish = Diamond Overlap CBN VS CONVENTIONAL (SURFACE FINISH – PLUNGE GRINDING ONLY) Nozzle increased production by 42% (762mm/min to >1,065mm/min.) + decrease dress amounts. “Automotive Valve Seats” 508mm x 458mm x 304.8mm Vitrified CBN wheel Thru-Feed Grinding Metal bond rotary dresser Dr. Webster Nozzle Each orifice is an oval 4mm 19 total orifices Hard Tuning Shafts to see if it was cost affective Cost was prohibitive because of tool life and change times the end